Hitherto, a photoresist composition comprising a photosensitive polyimide or a polyamic acid which is a precursor thereof, such a photoresist composition, which has mainly been used practically, is one which is coated on a substrate, light-exposed by the irradiation of an actinic light via a definite photomask, whereby the solubility of the light-exposed portions to a developer is reduced. The unexposed portions are dissolved and removed with the developer to thereby form a desired negative-type pattern on the substrate.
Because in the photoresist composition using photosensitive polyimide or the precursor thereof, which leaves the light-exposed portions with an actinic light on a substrate, the pattern obtained is excellent in the heat resistance, various kinds of the photoresist compositions have hitherto been proposed. For example, a method of introducing a methacryloyl group into the polyimide precursor via an ester bond or an ionic bond (as described in JP-A-49-11541, JP-A-50-40922, JP-A-54-145794, JP-A-56-38038, etc.) (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), a self-sensitizing-type polyimide having a benzophenone skeleton and having an alkyl group at the ortho-position to which a nitrogen atom is bonded (as described in JP-A-59-219330, JP-A-59-231533, etc.), etc., are proposed.
However, in the conventional negative-working photoresist composition comprising such a photosensitive polyimide or the precursor thereof, there are problems that the photoresist film is swelled with a developer at development and the light turns into at the light-exposure using a photomask to cause dissolution residues of the photoresist on the unexposed portions. Also, in the conventional negative-working photoresist composition, the shrinkage percentage of the film at hardening by heating is as large as about 50% and there is also a problem in the dimensional stability of the pattern obtained. Furthermore, because in the conventional photoresist composition, a developer containing an organic solvent is used, there is also a problem in the points of the working environment, the disposal of the waste solution, etc.
In addition, in the latter of the photoresist compositions described above, because the skeleton structure of the polymer is limited, the properties of the film finally obtained are subject to restriction and thus the polyimide cannot flexibly cope with various requirements.
Thus, the present inventors previously solved the above-described various problems in the negative-working photoresist composition comprising the conventional photosensitive polyamic acid by compounding the polyamic acid, which is a polyimide precursor, with a certain kind of a 1,4-dihydroxypyridine derivative forming a base having a pyridine skeleton by the irradiation of an actinic light as a photosensitive agent and clarified that a negative-working photoresist composition having a high sensitivity can be obtained as described in JP-A-6-75376.
However, in the negative-working photoresist composition, because the above-described 1,4-dihydroxypyridine derivative used as the photosensitive agent is insoluble in an aqueous alkali solution, an alcohol/water mixed solution of an alkali substance is used but in this case, depending on the component composition of the developer and the temperature of the development, the crystals of the above-described photosensitive agent sometimes deposit on the substrate during the development. When the crystals of the photosensitive agent deposit on the substrate, the development of a correct pattern is obstructed and also there is a possibility of lowering the resolving property by partially covering the developed fine pattern with the crystals. Furthermore, when the crystals deposited during the development attach to the photoresist film during the development and are still attached after rinsing, the crystals give bad influences on the film characteristics after hardening by heating. Also, in a cleaning process of the production of semiconductors, etc., such crystals cause a factor of lowering the cleaning extent as particles.
The present invention has been made for solving the above-described problems in the conventional negative-working photoresist composition comprising a photosensitive polyamic acid, and an object of the present invention is to provide a heat-resisting negative-working photoresist composition in which the structure of the polyamic acid as a heat-resisting resist-forming substance is not relatively restricted, and which is excellent in the sensitivity and the resolution and can be suitably used for practical production processes.
In particular, the present invention has been made for solving the problems described above in the conventional negative-working photoresist composition comprising a polyamic acid compounded with the above-described 1,4-dihydroxypyridine derivative as the photosensitive agent, and the object of the present invention is to provide a heat-resisting photosesitive composition comprising the photosensitive polyamic acid, which is not only excellent in the sensitivity and the resolution, but also can be easily developed with an aqueous alkali solution.
Furthermore, another object of the present invention is to provide a method of forming a negative-type pattern and a method of producing a circuit substrate using the above-described photoresist composition.